1. Field of the Invention
The present invention relates to a method of preparing a fry cooked product and fry cooking device.
2. Description of the Related Art
In fry cooking, it is important to make appropriate the quality of the fry cooked product and to supervise the quality of the fat/oil used for fry cooking.
Edible oil is subjected to chemical change such as decomposition and polymerization during fry cooking under the influences of the oxygen in the air, the heat generated from the heater, and water generated from the frying ingredients so as to give rise to deteriorated materials of the fat/oil such as free fatty acids, carbonyl compounds and polymerized matters. These deteriorated materials of the fat/oil are accumulated in the frying oil with process of the fry cooking time. Further, together with, for example, the frying refuse separated from the frying ingredients and the animal fat eluted from the frying ingredients, the deteriorated materials cause increases in the coloring, the viscosity, fuming and foaming of the frying oil. In addition, the frying oil is caused to generate an unpleasant odor and an unpleasant taste. The fry cooked product prepared by using such frying oil is rendered poor in flavor and presents an oily outer appearance so as to markedly lower the commercial value of the fry cooked product. Such being the situation, it is necessary to use all the time the frying oil having a low degree of deterioration.
In the conventional fry cooking apparatus (fryer), it is unavoidable for the frying oil to be deteriorated and for the deteriorated materials of the fat/oil to be accumulated. Under the circumstances, it was necessary in the past to discard entirely or partly the frying oil at the time when the degree of deterioration was increased to some extent and, then, to substitute a fresh frying oil. The discarding operation of the deteriorated frying oil is laborious. In addition, it is dangerous to discard the frying oil under the state of a high temperature because, for example, the operator is possibly scalded. What should also be considered is the disposal of the waste frying oil. In many cases, the disposal of the waste frying oil is consigned to the traders handling the waste oil. In recent years, the consignment fee is required and the consignment fee constitutes a big burden to the traders handling the fried food. Also, the requirement for the traders handling the fried food to suppress the generation of the waste frying oil is increased in view of the reduction of the industrial waste, too.
The method for decreasing the generation of the waste frying oil can be roughly classified into a method for suppressing the deterioration of the frying oil during the frying operation and a method for cleaning the deteriorated frying oil used for fry cooking. For suppressing the deterioration of the frying oil during the fry cooking, it is proposed to dip in the frying oil a porous material such as a ceramic material or calcined and powdered bones (Japanese Patent Disclosure (Kokai) No. 09-142950 and Japanese Patent Disclosure No. 62-101699). It is also proposed to apply voltage or current to the frying oil during the fry cooking (Japanese Patent Disclosure No. 09-100489 and Japanese Patent Disclosure No. 10-276744). However, with these methods, it is difficult to suppress effectively the deterioration of the frying, a high cost is required for introducing the apparatus and the running cost is high.
On the other hand, the method for cleaning the deteriorated frying oil has already been put to the practical use by, for example, utilizing the absorbing and filtering function performed by a porous body such as an activated charcoal or activated clay or by a filtering paper sheet of very fine meshes. This method produces a certain effect in respect of the removal of the fine fry refuse or the recovery of the color of the frying oil. However, the effect produced by this technology is much limited in respect of the removal of the fat/oil polymerized matters and the decomposed materials of the fat/oil generated in a large amount in the deteriorated frying oil (Japanese Patent Disclosure No. 6-166820 and Japanese Patent Disclosure No. 2000-178578).
Particularly, Japanese Patent Disclosure No. 62-220160 discloses, as a method of suppressing the deterioration of the frying oil, a cooking method in which the turnover rate of the frying oil, i.e., the frying amount per unit time (kg/hour) relative to the amount (liters) of the frying oil used, is set at 100%/hour or more, and a ratio of the contact area (cm2) of the frying oil with the air relative to the amount (liters) of the frying oil used, is set at 140 or less. However, it is well known in the art that the increase in the turnover rate of the frying oil and the decrease of the contact area of the frying oil with the air are effective for preventing the frying oil from being deteriorated. Also, it is certainly possible to increase the turnover rate of the frying oil to 100% or more in a large continuous fryer used in a food factory in which a large amount of frying ingredients are being fried continuously over a long time. However, it is substantially impossible to increase the turnover rate of the frying oil to 100% or more in a middle or small fryer used in a daily household dish store or a supermarket. Also, a ratio of the contact area (cm2) of the frying oil with the air to the amount (liters) of the frying oil used is not larger than 140 in almost all the cases in the middle and small fryers. It should be noted that the ratio noted above corresponds to a reciprocal number (1/H) of the depth (H) of the oil layer. It should also be noted that the prior art quoted above refers to all the fryers having the depth H of about 7.2 cm or more. In short, all the fryers fall within the range referred to in this prior art. It follows that this prior art does not suggest at all the technology for overcoming the problem in respect of the deterioration of the frying oil based on, for example, the shape of the oil layer.
Thus, an object of the present invention is to provide a method of preparing a fry cooked product, which permits maintaining the quality of the fat/oil by suppressing the elevation in the concentration of the deteriorated material in the fat/oil used for fry cooking, and which also permits maintaining appropriately the quality of the fry cooked product. Another object of the present invention is to provide a fry cooking device that permits the cooking method employed in the present invention to be worked suitably.